Systems for the deposition of drops of adhesive, conductive epoxy, soldering paste, and other viscous fluids at discrete locations on various surfaces are extensively used in modern manufacturing techniques and complex computer systems have been developed for directing the fluid dispenser to precise locations on any surface.
The fluid dispenser is generally comprised of a large syringe for storing the viscous fluid which is pneumatically forced into a small pump chamber, a reciprocating pump with a piston rod or needle that passes through the chamber and drives the fluid out of a small tubular dispensing tip. These fluid dispensers are quite satisfactory provided the fluid is of consistent viscosity and do not contain air because minute gas bubbles in a fluid compress causing sputtering and an uneven deposition.
The invention to be described is for a viscous fluid dispensing pump having a rotary feed screw for driving the viscous fluid out of the small dispensing tip. The rotary screw, which is driven by a servo motor, has a continually reducing variable pitch which acts to homogenize low viscosity components, such as trapped gas, with the relatively high viscosity material having a viscosity in the order of 5000 or more centipoise. As the viscous material enters, the volume between the threads and the cylinder wall is relatively large. As the material progresses the variable pitch of the screw causes the material to compress and mix as the volume reduces. The servo motor gives an accurate control of the amount of rotation of the screw and hence the output of the pump and also give the ability to vary the feed rate, hence makes the system easily adaptable to complete computer control.
A second embodiment is described, which operates on the same principle and is easier to manufacture, employs a rotary screw having linear threads but with a tapered or conical diameter.